Custom Object Wide Roles

Can we create custom object wide roles? In the same manner that db_datareader in effect grants SELECT on all tables, can we create roles that affect all objects without having to explicitly grant the permission on every object?

Yes, you can create a role and grant to it SELECT on the database, that is actually how db_datareader works as well. You can grant permissions on containers and they will apply to the contained objects. Databases and schemas are such containers.

Thanks
Laurentiu